Metal to screen seal for spinnerets



April 12, 1966 T. D. WILLIAMSON 3,245,112

METAL TO SCREEN SEAL FOR SPINNERETS Filed June 27, 1963 I NV ENTOR mam/1s a. WALL/4mm United States Patent 0..

This invention relates-to an improvedextrusion apparatus for use in shaping Off structures from solutions: of

synthetic polymers. More particularly, this inventionrelates to an improvedsealingand filtration-meansin an extrusion apparatus for use in the shaping of fibers and films from solutions of synthetic polymers.

Shaping of structures such asfibersand films from solutions of synthetic polymers generally'requires use of very small extrusion orifices, acioss which a large pressure drop is taken. Such a large; pressure drop is necessary to assure a uniform distribution of flow toeach hole in a spinneret as in fiber spinning and along theentire-length of a slot in castingoffilrns,

Filters of various types immediately upstreamirom-the extrusion orifice are also necessary to assure presentation of a clean solution, to the orifices. Such filters entrap particulate matter at a point sufiiciently remote from any extrusion orifice that cross-flow of solution can occur downstream therefrom and preventdisproportionate solution flow from the extrusion assembly.

Adequate filtration can be provided, depending on the quality of the solution or, melt to be shaped and on the orifice employed, by use of a metallic wire screen of suitable pore size or by use of; a woven fabric or felt cloth of nautral or synthetic fibers. When fibrous filters are used, a metallic wire screen is generally employed as the final element in a filtration assembly to provide mechanical support for the fi'brousfilters. and to provide for crossfiow of solution immediately upstream from the extrusion orifices which assures a uniform supply of solution thereto. i

The metallic wire screen edges rnust be sealed to the extrusion apparatus. This is necessary to prevent bypassing of unfiltered solution. Heretofore, such sealing has ken, the. form. of. a e astom e or de mab e m tallic gasket rnoldedto or mechanically crimped.v ar und the edges of the screen. Neither ofi'these means is cornr y sati actory- T e. tormer ontr u t o fic plugging as they distintegrate; under solvent attack. The latter. will notrecover from, the; deforming compression.

Wh n it i desir d t n o por the. ep a e haracteristics oftvvo individual polymericyspecies into, one, filamen ry structure, it is requ nt y a v ntag usto spin the two polymeric species in such a way that each species remains separate and distinctwithin a. diiferent area 01f the fi ber cross section. is particularly true when the difierences in properties of the two species are such as to p ce. a ri ped er when he w t r gies, are p n in eccentric relationship. to each other. For example, when two polymeric specie-s having different shrinkage characteristics appear in eccentric relationship to each other in a single fiber, that fiber will develop a desirable spiral-type crimp when it is treated under conditions which cause the two components to shrink.

Various embodiments of apparatus for producing composite or side-by-side fibers from two separate solutions or melts which are capable of forming fibers on evaporation, coagulation, or cooling are described in U .8. Patent 3,006,028. However, such apparatus has not proved to be satisfactory in providing fibers having a high degree of uniformity of distribution of components in the fiber structure since it would impracticably difficult to utilize elastorneric seals to provide a positive seal between the 3,245,112 [Ce Paten e Ann 12., 96

solution divider-s of the back plate and the face of the extrusion plate. Lack of such a gasket allows premature intermixing of the solutions causingthe formation of homopolymer fibers instead of bicomponent polymeric fibers or films.

It is, therefore, an object of this invention to provide an improvedapparat-us forfiltration of; synthetic-polymer solutions priorto extrusion through shaping orifices in an extrusion assembly,

Another object i's to provide an apparatus capable of producing a positive seal between the back plate and the face of the extrusion plate.

A further object is to provide an improved apparatus for cross-flow of solution immediately upstream from the extrusion orificeswhich assures a uniform supply-of solution thereto;

These and other objects will become apparent in the course of the following specification and claims.

The objects of this-invention are accomplished by an extrusion apparatus rfor producing shaped structures which comprises aback plate havingiat least one polymer receiving chamber, extrusion plate having at least one; orifice positionedin such a manner as to provide communication between said back plate chamber and said extrusionplate orifice, a1 fine mesh metallic sealing means positioned in compressed contactbetween saidback plate andsaid extrusionplate, to provide a positive seal between saidbackplate, and said extrusion plate and to provide for filtration ofxmaterials prior to their entrance into said extrusion plate orifice, and conduit; means having at least one channel, said channel being associated. in such a man-. ner with said back plate chamber for introducing-filamentforming materials into the said chamber.

This invention will be further illustrated by reference to the accompanyingdrawing inwhich:

FIGUREI represents a sectional view of one form of the improvedapparatus according to this inveniton.

FIGURE 2' is, an enlarged sectional] view of the QHCII-e clad, section of FIGURE 1 FIGURE 3 is an enlarged c ossrsectionalfview. similar to that of' FIGURE Z'but illustratingmodification to the apparatus of that figure to provide for spinning of filaments comprising two different synthetic polymeric mate-; rials.

FIGURE 4' is aschemati'c view ofa portion .of the face of the extrusion plate of FIGURE 1", illustrating the approximate proximity of extrusion, orifices contained therein,

With reference to FIGURE 1, the fluid fiber forming polymer substance either as a melt or inthe form of a solution is delivered through conduit lfinto chamber 2- above optional filter pack 3. After passage through the filter pack 3, if used; and multiple conduits 4, the polymer is filtered through die-cut screen '5 and extruded from multiple orifices 6.

As detailed in FIGURE 2 screen 5' is compressed at points Y'and Z between extrusion plate 7 'andback plate 8. u i y o be m de mp r ous o e. P y e at two concentric circles of contact. In this manner, bypassage of the screen by unfiltered solution is efiectively prevented.

FIGURE ,3 illustrates modifications to the detail of FIGURE 2 for spinning of two-component composite filamnts from three concentric rings or" orifices. Polymer A, as designated in the drawing of FIGURE 3, is delivered through conduits, not shown, to two annular dis tribution channels 9, while polymer B, as designated in the drawing of FIGURE 3, is delivered to two other annular distribution channels 10. The two polymers alternate with each other radially Within the extrusion assembly. Polymer dividers or septa 13, which are integral parts of back plate 8, are accurately machined. to

bear simultaneously on screen 5 as the flat inner face of extrusion plate 7 is pressed into position against the screen by retaining ring 14 and washer 15. By careful control of over-all extrusion assembly dimensions and of rigidity of the extrusion plate 7, the necessary compression of the screen 5 to form an impermeable seal in the required multiplicity of circles is achieved.

In operation, two separate spinning solutions or melts are fed through metering pumps, not shown, into distribution channels 9 and 10. Each polymer has complete freedom of crossrfiow within the bounds of its chamber. The polymer then flows into the individual slots 12 which are centered over extrusion plate orifices 11. The two polymers merge at substantially the center of slots 12 and are extruded as a side-by-side composite filament from orifices 11.

Various modifications of the apparatus shown in FIG- URES 1, 2, 3 and 4 may be used in combination with the extrusion plate of the present invention. For example, the separators or septa need not be in concentric rings as shovm in the drawings, however, concentric rings are preferred, as in fiber spinning; whereas, concentric rings would not be preferred in film extrusion.

In apparatus having a number of concentric septa, the extrusion plate may be cup-shaped as shown in the drawings, or may be in the form of a flat plate. The extrusion plate can be supported at its center as well as around its periphery. If additional filtration of the spinning solutions or melts is desired, distribution channels 9 and may be provided with filtering material.

The number of septa is.likewise not critical. However, it has been found that the improved sealing means of this invention provides the greatest improvement in uniformity of the distribution of components in apparatus having a plurality of concentric septa.

The materials of construction of the screens are not critical and may be selected from any materials that are known to be satisfactory for the extrusion of either of the solutions or melts, such as titanium or stainless steel. In the case of acrylonitrile polymer solutions, it is generally desirable to use apparatus constructed of Type 316 stainless steel because this material shows a very low degree of corrosion under operating conditions. The essential requirement is that the screen be compressible to an essentially impervious structure by forces which can be developed in assembly of the extrusion apparatus. For example, a compression of .005" is adequate to prevent cross-flow of solution through a stainless steel screen of 200 mesh made of .0023" diameter wire and woven in a twill pattern. A twill weave stainless steel screen of 200 x 1500 mesh, identified as Micromesh, No. '15M10 and made by Multi-Metal Wire Cloth Co. become impervious to spinning solution when compressed only .002. Greater compressions are feasible, but the minimum compression which gives a good seal is preferred in order to minimize the structural requirements imposed by high screen compressions on the extrusion apparatus.

ponent present in each" fiber. In producing single-component fibers or films, the advantages of this invention are found in the convenience and economy of extrusion assembly maintenance. In producing bicomponent fibers, the advantages are found in the provision of a large number of short length seals between the extrusion plate orifices and the septa of the back plate, heretofore, impracticably difficult to achieve, to prevent premature intermingling of the two solutions or melts.

Although the invention has been illustrated in its application to processes for spinning or" fibers from polymer solutions or melts, it obviously has utility and may be employed in solution or meltcasting of films, particularly in processses for the production of fine gauge films which employ narrow extrusion orifices, without departing from the spirit and scope of the invention.

What is claimed is:

1. An extrusion apparatus for producing shaped structures which comprises a back plate having separate chambers therein, an extrusion plate having at least one orifice positioned in such a manner as to provide communication between said back plate chambers and said extrusion plate orifice, a fine mesh metallic screen positioned in compressed contact between said back plate and said extrusion at a point below said screen and contiguous to said ori- The apparatus of this invention is useful in producing homo or single-component fibers or films or composite fibers or films of two components having a high degree of uniformity with regard to the amount of each comfices, and conduit means having at least two separate channel systems, each such system being associated with at least one of the said back plate chambers for introducing filament-forming materials into each of the separate chambers.

, 2. The apparatus of claim 1 wherein said metallic sealing means is made of stainless steel.

3. The apparatus of claim 1 wherein said metallic sealing means is made of titanium.

References Cited by the Examiner UNITED STATES PATENTS 2,013,688 9/1935 Kinsella 18-8 2,030,972 2/1936 Dreyfus '188 2,051,861 8/1936 Jones 188 2,058,408 10/1936 Butler et al 188 2,814,851 12/1957 Hervey 188 2,883,261 4/1959 McGeorge 188 X 2,891,278 6/1959 Cook 18--8 2,988,420 6/1961 Ryan et a1 188 3,006,028 10/1961 Calhoun 188 FOREIGN PATENTS 1,248,593 11/1960- France.

I. SPENCER OVERHOLSER, Primary Examiner. 

1. AN EXTRUSION APPARATUS FOR PRODUCING SHAPED STRUCTURES WHICH COMPRISES A BACK PLATE HAVING SEPARATE CHAMBERS THEREIN, AN EXTRUSION PLATE HAVING AT LEAST ONE ORIFICE POSITIONED IN SUCH A MATTER AS TO PROVIDE COMMUNICATION BETWEEN SAID BACK PLATE CHAMBERS AND SAID EXTRUSION PLATE ORIFICE, A FINE MESH METALLIC SCREEN POSITIONED IN COMPRESSED CONTACT BETWEEN SAID BACK PLATE AND SAID EXTRUSION PLATE TO PROVIDE A POSITIVE SEAL BETWEEN SAID BACK PLATE AND SAID EXTRUSION PLATE AND TO PROVIDE FOR FILTRATION OF MATERIALS PRIOR TO THEIR ENTRANCE INTO SAID EXTRUSION PLATE ORIFICE, SEPTA DIVIDING THE SPACE BETWEEN SAID EXTRUSION PLATE AND SAID BACK PLATE CHAMBERS INTO A PLURALITY OF SEPARATE ZONES, SAID SEPTA HAVING A LENGTH RELATIVE TO SAID BACK PLATE SUFFICIENT TO COMPRESS SAID SCREEN TO 